Transpose

{
  "asOf": "2026-10-11T14:26:15.299Z",
  "chords": [
    {
      "input": "C",
      "output": "G"
    },
    {
      "input": "Am",
      "output": "Em"
    }
  ],
  "degraded": false,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "fromKey": "C major",
  "notChecked": [
    "voice leading, instrument range or capo positions",
    "whether a minor-key target should use the harmonic or melodic scale for spelling",
    "…1 more"
  ],
  "reasons": [
    "Spelling follows G major: chords inside the key use its scale spelling, others use its sharp or flat side."
  ],
  "semitones": 7,
  "source": "computed locally",
  "summary": "C Am F G7 -> G Em C D7 (+7 semitones).",
  "toKey": "G major",
  "transposed": [
    "G",
    "Em",
    "…2 more"
  ],
  "verdict": "TRANSPOSED"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://music-theory.x402tookit.com/transpose?fromKey=C&progression=C+Am+F+G7&toKey=G'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://music-theory.x402tookit.com/transpose?fromKey=C&progression=C+Am+F+G7&toKey=G' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fmusic-theory.x402tookit.com%2Ftranspose
const res = await pay("https://music-theory.x402tookit.com/transpose?fromKey=C&progression=C+Am+F+G7&toKey=G");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://music-theory.x402tookit.com/transpose?fromKey=C&progression=C+Am+F+G7&toKey=G")
    print(res.status_code, res.text)